Devices for temporal control of the propagation of electromagnetic radiation represent fundamental building blocks for many modern technologies. Where a single spatial dimension is involved, such as in the propagation of a fiber optic communications signal down an optical fiber, such control is commonly achieved by devices affecting the amplitude of the propagating light (e.g., OFF/ON). In that environment, one-dimensional electrooptical modulators are often used that are based on electrooptic and/or magnetooptic materials such as calcite, quartz, and lithium niobate that change their refractive index responsive to applied control signals, the materials being arranged into Mach-Zehnder interferometers (MZIs) or similar devices converting induced phase changes into amplitude changes by interference effects. Other one-dimensional electrooptical modulators include electroabsorption modulators variably absorbing the incident signal according to an applied electric field, and acoustic wave modulators using high-frequency sound traveling within a crystal or a planar wave guide to deflect light from one place to another. Among other issues, such as limited power-handling ability, the above modulators each have substantial bandwidth limitations, e.g., practical limits to the speed at which they can vary the output signal between ON and OFF. By way of example, the maximum bit rate of many of the above electrooptic/magnetooptic effect modulators, as well as many of the above electroabsorption modulators, is on the order of 10-40 GHz, while many acoustic wave modulators have an even lower maximum bit rate.
Where two spatial dimensions are involved, e.g., in the controlled propagation of electromagnetic wavefronts in imaging systems, devices for temporal control of the propagating radiation include liquid crystal-based spatial light modulators (SLMs) and microelectromechanical (MEMs)-based SLMs, each generally providing for pixelwise amplitude or phase modulation of the propagating radiation. Among other issues, each of these SLM types has substantial bandwidth limitations. Although some liquid-crystal SLMs may use optical control signals rather than electrical control signals, pixel response times are nevertheless on the order of microseconds (binary) or milliseconds (analog). Typical response times for so-called digital micromirror devices, one type of commercially available MEMs SLM, are on the order of microseconds. Other issues relating to the above devices for one- or two-dimensional control of propagating radiation include power consumption, power handling ability, size, and environmental considerations.
One particular scenario involving control of the propagation of electromagnetic radiation relates to coupling pump laser light into a target device. This can be a desirable objective in many cases, such as for optically pumping the core of an erbium-doped fiber amplifier (EDFA) using pump light from a semiconductor diode laser. In order to facilitate higher power (e.g., one watt or greater) without damaging the semiconductor diode laser, the facet of semiconductor diode laser is often made relatively large. The transverse spatial modes of the semiconductor diode laser can become quite irregular, and light can be emitted with a numerical aperture on the order of 0.3-0.4, for example. However, the EDFA core usually has a small circular mode and can only receive light with a smaller numerical aperture on the order of 0.2, for example. Coupling the pump light into the EDFA core using a tapered optical fiber and cylindrical lens can yield relatively low efficiencies. More generally, it may be a desirable objective to couple source radiation from a source device having a first transverse spatial mode pattern into a target device having a second transverse spatial mode pattern that may be substantially different than the first transverse spatial mode pattern.
Accordingly, in relation to at least one of the above one-dimensional and two-dimensional contexts, it would be desirable to control the propagation of electromagnetic radiation in a manner that at least partially resolves one or more of the above issues. It would be further desirable to provide one or more useful devices based on such control capabilities.